These files represent uncertainty surfaces accompanying the datasets
"Uncertainty in Historical Land Use Data for the U.S. 1940-2015",
contained in the dataverse  HISDAC-US: Historical Settlement Data Compilation for the United States  
(https://dataverse.harvard.edu/dataverse/hisdacus).

Reference:
Mc Shane, Caitlin M.; Leyk, Stefan,; Uhl, Johannes H., 2021, "Uncertainty surfaces accompanying the Land Use gridded surface series",
https://dataverse.harvard.edu/dataset.xhtml?persistentId=doi:10.7910/DVN/JXJ5WH, Harvard Dataverse.

The shapefiles in Uncertainty in Historical Land Use Data for the U.S. 1940-2015 represent the proportion of records at the county level (2010 census boundaries) had either one or both
attributes (i.e., land use & year built) for all records. Counties are used in order to include the records that have land use and/or temporal information but are not explicitly georeferenced 
in the ZTRAX database. Each surface in Uncertainty in Historical Land Use Data for the U.S. 1940-2015 represents the decadal proportions of completeness for all records. Files are named according 
to the years each shapefile describes e.g. "LuUncert_Count_1940_1949.shp" (meaning that values between 1940-1949 are summed up) is the county level shapefile that characterizes attribute uncertainty 
for the time period 1940-1949. 

Uncertainty in Historical Land Use Data for the U.S. 1940-2015
Abbreviations and explanations:
GR:			Geo-Referenced. Records are georeferenced if an explicit latitude and longitude is provided in ZTRAX.
MG:			Missing Grid-ID. Records without an explicit latitude and longitude, which could not be grid-indexed.

Fips_CumSum:	The cumulative sum of all records in ZTRAX per FIPS code per decade
Lu_CumSum:		The cumulative sum of all records per decade that had a land use attribute
Yr_CumSum:		The cumulative sum of all records per decade that had a built year attribute
LuPrpCmplt:		The completeness of the land use variable for decade
YrPrpCmplt:		The completeness of the built year variable for decade


Gridded Layers
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There are two directories containing gridded surfaces in the dataset 'Uncertainty in Historical Land Use Data for the U.S. 1940-2015', one entitled 'Pixel' and the other 'Excluded'.
The gridded surface in Uncertainty in Historical Land Use Data for the U.S. 1940-2015 entitled 'Pixel' represents the proportion of georeferenced records per grid cell with no land use information. Each gridded layer represents the decadal proportions
of georeferenced records per grid cell with no land use information. File are named according to the years each tif describes e.g. "LU_UncertPix_1940_1949.tif" is the gridded surface that characterizes the land use
attribute's missingness for the time period 1940-1949. In order to account for all georeferenced records that were missing the built year attribute, we included an additional gridded surface entitled
"LU_UncertPix_2016.tif" which represents the proportion of georeferenced records per grid cell that were missing either one or both attributes (i.e. land use & built year).

The gridded uncertainty layers capture attribute missingness through time, thus ‘no data’ cells are desirable in these layers as this means that attribute completeness for these cells is high per the data contained in ZTRAX. 
These layers are a useful measure of how many total structures are contained in a given grid cell for a specific point in time and how many of the structures - relative to the total count - have the land use attribute. 
These layers can be used to determine the data quality of primary gridded layers i.e. one can assess the proportion of structures containing both the year built and land use attributes and the proportion of structures 
in the same grid cell that are lacking attributes but are present in the data.

Uncertainty in Historical Land Use Data for the U.S. 1940-2015 (Pixel)
Abbreviations and explanations:

Geo-Referenced:	Records are georeferenced if an explicit latitude and longitude is provided in ZTRAX.
Missing Grid-ID:	Records without an explicit latitude and longitude, which could not be grid-indexed.
Grid Cell Value:	Proportion of georeferenced records with no land use information, but contain temporal information (i.e., built year information)
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The second gridded uncertainty layer contained in the directory entitled 'Excluded' captures the decadal cumulative sum of structures that were contained in ZTRAX and excluded from the
land use data represented in 'Historical Land Use for the U.S. 1940-2015' [Major Class & Class Counts]. The excluded structures come from 7 thematic land use types that are poorly 
represented in the ZTRAX database or characterized non-built up properties. The excluded categories are:

1. Exempt
2. Historical
3. Miscellaneous
4. Privately Owned
5. Transportation
6. Vacant
7. Agriculture: non-structural records were excluded from the agricultural class. There are 12 total agricultural sub-classes that were excluded from the data in order to ensure
                only built up properties were defined.

Uncertainty in Historical Land Use Data for the U.S. 1940-2015 (Excluded)
Abbreviations and explanations:

Geo-Referenced:	Records are georeferenced if an explicit latitude and longitude is provided in ZTRAX.
Grid Cell Value:	Cumulative sum of georeferenced records containing temporal information with a land use type excluded from the data


Data source: Zillow Transaction and Assessment Dataset (ZTRAX) (c) Zillow Inc.
Coordinate reference system:
USA Contiguous Albers Equal Area Conic USGS version (SR-ORG:7480)
https://spatialreference.org/ref/sr-org/usa_contiguous_albers_equal_area_conic_usgs_version-2/
Proj4: +proj=aea +lat_1=29.5 +lat_2=45.5 +lat_0=23.0 +lon_0=-96 +x_0=0 +y_0=0 +ellps=GRS80 +datum=NAD83 +units=m +no_defs

Contact:
Stefan Leyk
Department of Geography
University of Colorado Boulder
GUGG 110, 260 UCB 
Boulder, CO 80309-0260, United States of America
stefan.leyk@colorado.edu